In ITU-R (International Telecommunication Union Radio communication sector), a standardization task for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the third generation) is being in progress. IMT-Advanced sets its goal to support IP (Internet Protocol)-based multimedia service at the data transfer rate of 1 Gbps in the stop and slow-speed moving states and at the data transfer rate of 100 Mbps in the fast-speed moving state.
3GPP (3rd Generation Partnership Project) is a system standard to satisfy the requirements of IMT-Advanced, and it is preparing LTE-Advanced improved from LTE (Long Term Evolution) based on an OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission scheme. LTE-Advanced is one of the strong candidates for IMT-Advanced. Relay station technology is included in the major technology of LTE-Advance.
A relay station is an apparatus for relaying signals between a base station and a user equipment and is used to extend the cell coverage of a wireless communication system and improve the throughput.
The relay station is difficult to transmit and receive signals through transmission antennas and reception antennas using the same frequency band on the same time. In general, because power of a transmission signal transmitted by a relay station is much greater than power of a reception signal received by the relay station, the transmission signal of the relay station functions as interference for the reception signal and the reception signal may be distorted. This is called self-interference (SI). In order for the relay station to solve the self-interference problem, a complicated interference removal process is required, and transmission and reception signal processors need to be spatially separated from each other. It is practically very difficult for the relay station to remove self-interference. Although self-interference is removed, a lot of the costs will be consumed. It is therefore assumed that it is difficult for a relay station to transmit and receive signals using the same frequency band on the same time.
A relay station is difficult to perform data reception from a base station and data transmission to a user equipment (or data transmission to a base station and data reception from a user equipment) at the same time because of the self-interference problem. Cases where a relay operation is not guaranteed in the configuration of a specific radio frame may be generated.
In the prior art, in the case where a relay station transmits data to a base station in a certain subframe, the base station sets the relevant subframe as an uplink subframe, and the relay station sets the relevant subframe as an uplink subframe or an MBSFN (Multicast/Broadcast Single Frequency Network) subframe and then transmits the data. In accordance with this conventional method, for example, a radio frame configuration including only one uplink subframe within a radio frame, when a relay station transmits data to a base station using the uplink subframe, the relay station cannot receive data from a user equipment in the relevant uplink subframe. Consequently, in this radio frame configuration, the relay operation of the relay station is not guaranteed.
There is a need for a method of a relay station efficiently relaying data in a wireless communication system.